Microprocessors are general-purpose processors that provide high instruction throughputs in order to execute software running thereon, and can have a wide range of processing requirements depending on the particular software applications involved. Many different types of processors are known, of which microprocessors are but one example. For example, Digital Signal Processors (DSPs) are widely used, in particular for specific applications, such as mobile processing applications. DSPs are typically configured to optimize the performance of the applications concerned and to achieve this they employ more specialized execution units and instruction sets. Particularly in applications such as mobile telecommunications, but not exclusively, it is desirable to provide ever-increasing DSP performance while keeping power consumption as low as possible.
As the number of transistors incorporated into modern day integrated circuits increases, the power needed to drive these integrated circuits also increases. As this trend of packing more and more power-hungry transistors into a single integrated circuit continues, techniques to reduce the overall power consumed by these integrated circuits becomes more important.
As is well known, power consumption is related to the voltage level of the voltage supply as well as the frequency of operation by the following equation: P=CF(Vdd)2, where F is the operating frequency, C is the switched capacitance, and Vdd is the power supply voltage. As this equation demonstrates, power may be significantly reduced by lowering the voltage level of the supply voltage. Unfortunately, the maximum performance obtainable for a given operating frequency F is also related to the supply voltage as follows: Id(sat)=β(Vdd−Vt)α, where: Id(sat) is the drain current at saturation, Vdd is the drain-to-source voltage, and Vt is the threshold voltage. α is a process dependent parameter and is typically taken to be 2, but may be between one and two and β has its usual meaning, well known in the art, including the width and length parameters for an metal-oxide semiconductor (MOS) transistor. Consequently, because systems are designed to operate at a voltage level that meets their peak computational performance demands, they consume significant amounts of power that is not useful at times when the peak computational capability is not required. In such systems, power is typically saved by “clock gating.” In this approach, the sections of the device or system which are unused have the clocks that drive those sections turned “off.” This lowers the effective frequency of operation, resulting in a linear improvement, as indicated by the equation above, essentially by lowering the average frequency by including zero frequency time spans into the average.
U.S. Pat. No. 5,760,636 entitled “Adjusting Clock Frequency and Voltage Supplied to a Processor in a Computer System” describes a method and apparatus for adjusting the clock frequency and voltage supplied to an integrated circuit in which a signal is first sent to the clock, and in response, the clock lowers the clock frequency supplied to the integrated circuit. The clock sends a signal to the voltage regulator whereupon the voltage regulator reduces the voltage supplied to the integrated circuit. The regulator sends a signal to the clock that is used to ensure the clock frequency is reduced or increased during the transition periods only when the voltage regulator supplies a high voltage to the processor.
U.S. Pat. No. 6,425,086 entitled “Method And Apparatus For Dynamic Power Control Of A Low Power Processor” describes a system in which a voltage regulator includes a control register. Processor instructions being executed by the processor may provide binary digital signals to the control register which results in the operating voltage of the processor being changed by the voltage regulator.
Still, a need exists for a technique that improves the reduction in power consumption for these low power requirement conditions, while still delivering sufficient computational performance to complete the tasks during high power requirement conditions.